1. Field of the Invention
The present invention relates to a feed for relieving stress and a method of relieving stress. More specifically, it relates to a stress-relieving feed for livestock or poultry which comprises yeast rich in glutathione or a mixture of glutathione and yeast, and a method of relieving stress which comprises feeding to livestock or poultry yeast rich in glutathione or a mixture of glutathione and yeast.
2. Description of the Related Art
The present days are called the age of stress. Stress is a serious problem for not only humans but also animals.
Stress of livestock such as cattle, hogs, fowls, and horses is caused by the environment of their stalls including the physical environment such as temperature and humidity, and the biological environment such as pathogenic microbes and relationship between animals, which results in an inhibition of generative function, a decline of productivity, an increase in the occurrence of diseases, and a formation of stomach ulcer. Upon transportation, animals suffer from extreme stress attributed to fatigue caused by jolting on the truck, excitement resulted from encountering with other cattle, hogs and the like, a sudden change of an external environment such as coldness and heat. As a result, such stress may cause them infectious diseases, among which pneumonia is a main disease, and diarrhea. There is a report that, when cattle are transported by truck, it leads to changes in cell-mediated immunity including a rise of a plasma cortisol level, an increase of the number of white blood cells, and a selective decline of T-lymphocytes (Proc. Jpn. Anim. Biochem., 20, 59.67 1987).
In the case of livestock for meat, quality of meat is sometimes deteriorated from stress which is caused by cutting off of supply of feeds and water after brought into a slaughterhouse, confinement under overcrowded conditions, and chasing by force immediately before slaughter, in addition to transportation before slaughter.
Recently, people who are feeding pets in their apartments are increasing. Since a sphere of action of such pets is limited to small rooms, they cannot freely go outside and cannot communicate with other individuals. Thus, they suffer from stress, which makes them run about the rooms. Dogs often howl, while cats often sharpen their claws upon a post or furniture. Such abnormal behaviors attributed to stress caused by environment are observed among animals in the zoo. For example, tongue playing is known. It is often seen that giraffes in the zoo put out and pull in their slender tongues at a momentary speed. This behavior is not seen for giraffes which live wild lives in a vast grassy plain. Accordingly, it is said that the cause of the behavior is stress resulted from that they are confined in a small cage and are deprived of their free lives.
In order to prevent such problems caused by stress, for example, to prevent deterioration of quality of pork, some meat centers give such guidance in a system to slaughter hogs as to change the conventional strainer with V-shape guide way to the mobile floor conveyer system, and to adjust the period from the last feeding to slaughter to within 30 hours, in a transportation system as to change the materials of the floor of trucks to non-slippery ones, to make compartments, and to make a plan for an animal-collecting schedule which makes the transportation period shorter.
Though there are considered many stressors for stress derived from the feeding management of livestock, any reform measure has not been taken. This is because most of stressors relate to the feeding facilities such as materials of the floor and spatial extent of stockades, and therefore it costs a great deal to effect reformation. Concerning the transportation system for livestock, its improvement requires reformation of trucks, and it takes great expense in one lot. Further, in the case of livestock for meat, the collection areas are expanding in keeping with facilities and magnification of the slaughterhouse, which necessarily makes the transportation period longer. Though some meat centers give guidance as described above, it is difficult for them to guide all of farms thoroughly because the areas are expanding. Thus, they can guide very few farms through the country.